To size a power supply you must match the supply voltage to the voltage of your outputs. You must also add up the wattages of all the outputs that will be on at any given time, as well as any watts required by the controller and it's internal amplifier.

Voltage
Determine the voltage of your output devices, generally these are solenoids or relays. The voltage must be 12 or 24 volts DC to be used with our solid-state output products. The voltage of your power supply MUST match the voltage of your output devices!

Choosing a Voltage
We used to recommend using 24 volt power supplies with the Flex and FlexMax. This was because each output was limited to 500mA of current. So 24 volts allowed up to 12 watts per output where 12 volts allowed only 6. The new high-capacity solid-state outputs on the current models make that concern a thing of the past. Feel free to use 12 or 24 volts depending on what devices you are controlling.

Another factor to consider when choosing a voltage is the product's internal amplifier. The FlexMax's amplifier will be loudest at 24 volts. It's still pretty loud at 12, but it can only give you the full 50 watts at 24 volts. Please note that the PicoBoo amplifiers can only handle 12 volts, using a 24 volt supply on those will burn them out.

Wattage
The wattage of your supply must meet or exceed the total wattage required by all your outputs plus the controller and its internal amplifier if it has one. To do this, add up the wattage of all your valves, this should be clearly marked on the label of each valve, 5 to 6 watts is common. You may not have all the outputs turned on at any one time, so you can cheat a bit here. Add up the wattages of the most outputs that will be turned on at any given time. Now add the wattage for your controller, 3 watts is a safe bet here. If your controller has an internal amplifier, add up the wattage of that too. That's 50 watts for the FlexMax's amplifier.

Example 1
Let's say you have six 24VDC 6 watt valves connected to a controller, but a maximum of three of them will be turned on at any given time.

18 watts (3 x 6 watt solenoid valves)
3 watts (controller)
------------------
21 watts total

Example 2
Let's say you have twelve 24VDC 6 watt valves connected to a FlexMax, a maximum of nine of them will be turned on at any given time. We will be using the internal amplifier as well.

54 watts (9 x 6 watt solenoid valves)
3 watts (FlexMax)
50 watts (FlexMax amplifier)
------------------
107 watts total

Common Solenoid Wattages
MAC Valve 3-Way 1/8" Port: 12v = 5.4 watts / 24v = 5.4 watts
MAC Valve 3-Way 1/4" Port: 12v = 8.5 watts / 24v = 6 watts
MAC Valve 3-Way 3/8" Port: 12v = 6 watts / 24v = 6 watts
MAC Valve 3-Way 1/2" Port: 12v = 6 watts / 24v = 6 watts